THE VEINS OF THE HEAD AND NECK. 513 



wards and enters the upper part of the large azygos vein; that of the left 

 side usually passes forwards across the highest part of the arch of the aorta 

 and joins the left innominate vein ; it also communicates below with the . 

 commencement of the left upper azygos vein, and sometimes it passes entirely 

 into this vessel. 



Varieties of the superior vena cava and innominate veins. A considerable number 

 of instances are recorded in which, the left innominate vein, being 1 formed in the usual 

 manner, does not cross the middle line to join the corresponding vessel of the right side, but 

 is continued down in front of the arch of the aorta and the root of the left lung to the heart, 

 where it receives the great cardiac vein and then inclines outwards in the usual position of 

 the coronary sinus to open into the right auricle, thus giving rise to what has been termed a 

 left superior vena cava. In some of these cases the right and left veins are connected by a 

 cross branch of small size in the usual position of the left innominate vein. This condition 

 is normal in many animals, and its occurrence in the human subject is due, as is fully 

 explained in the description of the mode of development of the great veins, to the persistence 

 of the communication between the left primitive jugular vein and duct of Cuvier in the 

 foetus. A trace of this connection is frequently to be seen in the adult in the form of a 

 small fibrous cord passing from the left superior intercostal vein as it crosses the aorta, 

 within the vestigial fold of the pericardium, to the commencement of the oblique vein on the 

 back of the left auricle (p. 353). In a few cases such a left superior vena cava has been 

 found opening into the left auricle of the heart ; and in two instances the coronary sinus has 

 been observed terminating in a similar manner (Lindner, Jeffrey). 



Five examples of a single left superior vena cava, without transposition of the viscera, 

 have been met with, the right innominate vein crossing the middle line and joining the 

 vessel of the left side to form a trunk which has a disposition similar to that of the left 

 superior vena cava described above. In these cases the left duct of Cuvier has remained 

 patent and undergone development, while the channel of the right side has become occluded. 



Another form of persistence of the left duct of Cuvier has been met with by Gruber ; in 

 this the opening into the right auricle is occluded, and the principal veins of the heart 

 terminate in a trunk which ascends to the left innominate vein (Virchow's Archiv, xcix). 



VEINS OF THE HEAD AND NECK. 



The blood returning from the head and neck flows on each side into two prin- 

 cipal veins, the external and internal jugular. There are generally no valves in 

 the veins of the head and neck, except at the lower ends of the external and internal 

 jugular veins, near their junction with the subclavian, where valves are always present. 



The superficial veins of the fore part of the head and the deep veins of the face 

 converge and unite so as to form two principal trunks, the facial and temporo- 

 maxillary veins. From the hinder part of the scalp the blood is collected by the 

 posterior auricular and occipital veins. 



The facial vein (anterior facial) lies obliquely along the side of the face, 

 extending from the inner margin of the orbit downwards and outwards to the 

 anterior border of the masseter muscle. Resting on the same plane as the facial 

 artery, but being placed farther back, and taking a less tortuous course, it has very 

 nearly the same relations to contiguous parts. It commences at the side of the nose 

 by a vein termed angular, which collects blood fyom the forehead, the upper eyelid 

 and the nose, and it is increased in size by the junction of numerous tributaries on 

 its way downwards. Below the jaw it inclines backwards, covered by the cervical 

 fascia and the platysma myoides, and unites below the digastric muscle with the 

 anterior division of the temporo-maxillary vein to form a short trunk (common 

 facial vein), which opens into the internal jugular about the level of the hyoid bone. 

 From the facial vein near its ending a communicating branch generally runs down- 

 wards along the anterior border of the sterno-mastoid muscle to join the lower part 

 of the anterior jugular vein. 



Tributaries. (a) The frontal vein is formed by branches which pass obliquely 

 downwards and inwards from the roof of the skull and the forehead, maintaining 



